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Signaling Architecture and Protocols for the Next
Generation Network
Hyeong Ho Lee
Electronics and Telecommunications Research Institute (ETRI), [email protected]
Abstract ITU-T (International Telecommunication
Union, Telecommunication Standardization Sector) made
remarkable achievement in international standardization
of the Next Generation Network (NGN) during the last
Study Period (2005~2008). This paper gives a brief
overview and functional architecture of ITU-T NGN, and
presents signaling architecture and protocols for the
ITU-T NGN.
Keywords NGN, Signaling, Protocol, ITU-T.
1. Introduction
During the last study period (2005~2008) of ITU-T,ITU-T made remarkable achievement in internationalstandardization of the Next Generation Network(NGN).
The NGN defined by ITU-T is a packet-based network
able to provide Telecommunication Services to users
and able to make use of multiple broadband,
QoS-enabled transport technologies and in which
service-related functions are independent of the
underlying transport-related technologies. It enables
unfettered access for users to networks and to
competing service providers and services of their choice.It supports generalized mobility which will allow
consistent and ubiquitous provision of services to users
[1]. NGN services include multimedia services, such as
conversational services, and content delivery services,
such as video streaming and broadcasting. The aim of
NGN is to support PSTN/ISDN replacement. Therefore,
the NGN provides support for PSTN/ISDN emulation as
well as PSTN/ISDN simulation. NGN Release 1
assumes the implementation of session-based
communication. Release 2 aims for the provision of
IPTV (Internet protocol television) and implementation
of true mobility.
ITU-T formed NGN-related joint Study Group (SG)
system that included Study Groups such as SG13 (Next
Generation Network), SG11 (signaling protocols),
SG19 (mobile networks), and SG17 (security issues),
and has been holding regular meeting called the NGN
Global Standards Initiative (NGN-GSI) since 2006. As
a result, ITU-T produced Recommendations related to
the NGN such as ITU-T Rec. Y.2000-series,
Q.1700-series, and Q.3000-series.
Following this introduction, we explain overview and
functional architecture of the NGN in Section 2, andsignaling architecture and protocols for the NGN in
Section 3, and then finally describe concept of the NGN
Protocol Set, future work, and conclusion.
2.NGN Architecture
NGN shall provide the capabilities (infrastructure,
protocols, etc.) to make the creation, deployment and
management of all kinds of services (known or not yet
known) possible. This comprises of services using
different kinds of media (audio, visual, audiovisual),
with all kinds of encoding schemes and data services,
conversational, unicast, multicast and broadcast,
messaging, simple data transfer services, real-time and
non-real-time, delay-sensitive and delay-tolerant
services.
NGN should be comprised of service related APIs
(Application Programming Interfaces) in order to
support the creation, provisioning and management ofservices. One of the main characteristics of NGN is the
decoupling of services and transport, allowing them to
be offered separately and to evolve independently.
Therefore in the NGN architectures, there shall be a
clear separation between the functions for the services
and the functions for the transport. NGN allows the
provisioning of both existing and new services
independently of the network and the access type used.
In NGN the functional entities controlling policy,
sessions, media, resources, service delivery, security,
etc., may be distributed over the infrastructure,
including both existing and new networks. When they
are physically distributed, they communicate over open
interfaces. Consequently, the identification of reference
points is an important aspect of NGN. Protocols need to
be standardized to provide the communication between
communicating functional entities. Interworkingbetween NGNs of different operators and between NGN
and existing networks such as PSTN (Public Switched
Telephone Network), ISDN (Integrated Services Digital
Network) and GSM (Global System for Mobile
communications) is provided by means of gateways.
NGN will support both existing and "NGN aware" end
terminal devices. Hence terminals connected to NGN
will include analogue telephone sets, fax machines,
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ISDN sets, cellular mobile phones, GPRS (General
Packet Radio Service) terminal devices, SIP [2]
(Session Initiation Protocol) terminals, Ethernet phones
through PCs (Personal Computers), digital set top boxes,
cable modems, etc.
Overview of the NGN architecture
Figure 1 shows an overview of the NGN functionalarchitecture that allows the support of the Release 1
services [3], [4], [5]. The NGN functions are divided
into service stratum functions and transport stratum
functions. An NGN communication service is
implemented by integrating these two functions.
The service stratum provides a variety of functions ascommunication services such as user authenticationand registration, party discovery, and call condition
negotiation as well as supplementary services to
support and enhance those services. The transport
stratum provides IP connectivity services to NGN users
under the control of transport control functions. It
transmits IP packets on an end-to-end basis whilemaintaining QoS and providing security. Theconnection points specified between the NGN and theoutside world are the User-Network Interface (UNI)for terminal connections, the Network-NetworkInterface (NNI) for connection with other NGNnetworks, and the Application-Network Interface
(ANI) for connection to applications.
Figure 1 NGN Architecture Overview
The service stratum provides Service ControlFunctions (SCF) to achieve basic communication
services. For this purpose, the ITU-T Recommendationallows the implementation of call-server models as well
as the IP Multimedia Subsystem (IMS) using session
initiation protocol (SIP). The transport stratumprovides Network Attachment Control Functions(NACF) and Resource Admission Control Function(RACF). NACF performs functions such as IP-addressassignment, authentication, and registration of user andterminal. RACF decides, based onnetwork availability,
whether each session setup request to be accepted and,
if accepted, guarantees a stable level of communication
quality until the session ends.
Generalized NGN functional architectureThe generalized NGN functional architecture shown in
Figure 2 [3] is based on the NGN architecture overview.
In this functional architecture, some Functional Entities
(FEs) include functions relating to the NGN servicestratum and the NGN transport stratum. The transport
stratum covers transport functions and associated
control functions up to the IP layer, and the service
stratum includes functions that handle the layers above
the IP layer. There are relationships between end-user
functions and the transport stratum such as IP-based
relationships, PSTN/ISDN relationships related to
media transport, and some signaling relationships. The
relationships between the end-user functions and
service functions represent service protocol layer
relationships. The relationships to the application
functions represent application layer protocol
relationships.
3.NGN Signaling Architecture andProtocols
Based on the NGN functional architecture, ITU-T SG11
has been studying the NGN signaling system, focusing
on NGN signaling requirements and architecture and
protocols at internal and external interfaces of the NGN
system. The major achievement is the completion and
publication of some twenty Recommendations that
constitute the NGN Protocol Set 1. They constitute a
fundamental basis for initial implementations of first
release of NGN.
Principles of MappingConsiderations of scalability and domain independence
that motivated the development of the functional
architecture have been accepted for the realization of
NGN signaling system. As a result, each Functional
Entity (FE) of the functional architecture is mapped to a
separate type of Physical Entity (PE) [6]. Furthermore,
each reference point is assumed to map to a separate
interface. At a particular interface, one protocol from a
set of recommended protocols may be used. Because the
mapping between reference points and interfaces is
one-to-one, each interface is named after the reference
point to which it corresponds (e.g., Rs interface
corresponding to the Rs reference point).
Depending on the technology involved, some of the
physical entities may be combined. In such a case, each
combined entity will support the combined set of
external interfaces of its component elements, and
interfaces that would lie between the component
elements if they were separate are absorbed into the
interior of the combined entity
Signaling Architecture for NGN SCF
Transport stratum
Service stratum
Control
Media
ManagementFunctions
Management
ANI
Transport Control Functions
Resource andAdmission
Control Functions
Network AttachmentControl Functions
Network AttachmentControl Functions
NNIUNI
Application Support Functions & Service Support Functions
Applications
Transport Functions
End-User
FunctionsOther
Networks
Service Control
FunctionsService User
ProfilesService User
Profiles
Transport UserProfiles
Transport UserProfiles
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Based on the principles of mapping, it identifies the
Physical Entities (PEs), interfaces, and protocols that
are required to model the SCE of the NGN [7]. This
service control architecture supports SIP-based sessions
and is independent of services.
Table 1 shows the interfaces of service control entity
and candidate protocols potentially for use in these
interfaces. For example, Recommendations ITU-T
Q.3401 and Amendment 1 to Q.3401 define the NGN
NNI signaling profile (SIP/SDP and RTP profile) for the
SCF at the NNI interface, between two NGN network
operators, for voiceband, video, and data services.
Recommendation ITU-T Q.3402 defines the NGN UNI
signaling profile (SIP/SDP and RTP profile) for use
between users and networks for voice, video and data
services.
Table 1. Interfaces and Protocols of SCE
Interfaces Protocols
A-S1 (S-14 MRB-FEASF/SSF) SIP, SOAP,HTTP
A-S3 (S-13 MRC-FEASF/SSF) SIP
A-S4 (S-1 S-CSC-FEASF/SSF) SIP
A-S5 (S-6 SAA-FEASF/SSF) Diameter
A-S6 (S-4 SL-FEASF/SSF) Diameter
A-S6 (S-5 SUP-FEASF/SSF) Diameter
S-1 S-3, S-1 S-2, S-2 S-3, S-1 S-7, S-2
S-7, S-3 S-7, S-7 S-10, S-1 S-10, S-3 S-10, S-2 S-10, S-1 S-9, S-3 S-9, S-1
S-13, S-2 S-13, S-7 S-13, S-9 S-10, S-2 S-11, S-7 S-12, S-10 S-10, S-1 S-8,
S-3 S-8, S-9 S-13, S-13 S-10
SIP
S-1 S-5, S-1 S-6, S-3 S-5, S-3 S-6, S-1
S-4, S-3 S-4
Diameter
S-9 T-7, S-13 T-8, S-7 T-6, S-8 T-1 H.248
S-2 T-16, S-7 T-16, S-8 T-16, S-2 T-13
Diameter
S-9 T-9 SS7 over IP
S-9 End user function SIP
S-11 End user function -
S-7, S-10 other NGN/IP multimediaNetworks
SIP
S-12 other NGN/IP multimedia Networks -
NOTES:SIP: Session Initiation Protocol [IETF RFC 3261] [2]
SOAP: Simple Object Access Protocol [W3C Rec. (2007)] [8]HTTP: Hypertext Transfer Protocol [IETF RFC 2616] [9]
Diameter: Diameter Base Protocol [IETF RFC 3588] [10]H.248: Gateway Control Protocol: Version 3 [ITU-T Rec. H.248
(09/2005)] [11]
SS7: Signaling System No.7 [ITU-T Rec. Q.700 (03/1993)] [12]
Signaling Architecture for NGN RACFThe signaling architecture for the NGN Resource and
Admission Control Entity (RACE) is based on the
RACF of which generic functional architecture is shown
in Figure 4 [13], [14]. Based on the principles of
mapping, it identifies the Physical Entities (PEs),
interfaces, and protocols that are required to model the
RACE of the NGN [6]. Table 2 provides mapping
between the interfaces and the protocol specifications
which realize these interfaces. Recommendations
ITU-T Q.3300-series specify signaling and protocols at
the interfaces for RACF.
Figure 4. Generic Functional architecture for resource
and admission control in NGN
Table 2. Interfaces and Protocols of RACE
Interfaces Protocols
Rs, Rt, Rd, Ri Diameter
Rp RCIP
RwCOPS-PR
H.248
Diameter
Rc COPS-PR
SNMP
Rn Interface is for further
study
NOTES:
Diameter: Diameter Base Protocol [IETF RFC 3588] [10]
RCIP: Resource Connection Initiation Protocol [ITU-T Rec.
Q.3302.1 (03/2007)] [15]
COPS-PR: Common Open Policy Service Policy Provisioning[IETF RFCs 2748, 3084] [16], [17]
SNMP: Simple Network Management Protocol [IETF RFC 3410
and many others] [18]
Signaling Architecture for NGN NACFThe signaling architecture for the NGN Network Access
Control (NACE) is based on the NACF of which
generic functional architecture is shown in Figure 5
[19]. Based on the principles of mapping, it identifies
the Physical Entities (PEs), interfaces, and protocols
that are required to model the NACE of the NGN. Table
3 shows the interfaces of NACE and candidate protocols
potentially for use in these interfaces.
Recommendations ITU-T Q.3200-series specify
signaling and protocols at the interfaces for NACF.
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Transport Functions
OtherNGNs
PD-FE
AR-FE
CPE
HGWC-FE
TUP-FE
AM-FE
NAC-FE
TC-Ux
TC-T1
Na Nd
Nk
NeNc
Nb
Nx
Service Control Functions
S-TC1
TAA-FE
Ni
TLM-FE
Ng
T-U1
TE HGW
RACFNACF
PE-FE
Ru
Figure 5. Generic Functional Architecture for Network
Attachment Control in NGN
Table 3. Interfaces and Protocols of NACE
Interfaces Protocols
Ng, Ru, S-TC1 Diameter
NiRADIUS or DiameterTo be selected
Nd, Ne, Na, Nc, Nk, Nx,Nb, TU1, TC-T1, TC-Ux
Interface is for furtherstudy
NOTES:
Diameter: Diameter Base Protocol [IETF RFC 3588] [10]RADIUS: Remote Authentication Dial In User Service [IETF
RFC 2865] [20]
4. Concept of NGN Protocol Set
NGN Release and Capability SetIn the last Study Period (2005~2008), ITU-T SG13 had
adopted a release-based approach for the production of
NGN Recommendations, with the scope of each release
clearly defined and target deadlines for completionspecified. Considering a priority of a market, ITU-T
SG13 has adopted the concept of Capability Set that
breaks down the release concept because necessary
functional groups exist prior to a target completion date
of Release. Capability Set includes requirements,
architecture, and signaling aspects necessary to provide
specific services. Release concept determines the scope
of standardization in ITU and Capability Set specifies
related Recommendations necessary for specific
services [21].
ITU-T SG13 produced Recommendation Y.2006
(Description of capability set 1 of NGN release 1), and
is now developing a new draft RecommendationY.NGN-cap2 (Description of NGN capability set 2).
NGN Capability Set 1 is mainly focused on basic
telecommunication services. Since Capability Set 1 is a
basic set of telecommunication, all the items that are
covered in Capability Set 1 should be included in
Capability Set 2. In addition, NGN Capability Set 2
should include the items that are necessary to provide
IPTV service.
A given specification of a given NGN Release can be
categorized using three stages: service aspects (Stage 1),
functional network aspects (Stage 2) and network
implementation aspects (Stage 3). Whilst in principle,
all services and capabilities defined in a given capability
set of the NGN Release are to be specified to the Stage 3
level to ensure that the release is fully implementable,exceptions can be accepted.
NGN Protocol SetIn the last Study Period, the NGN Protocol Set 1 was a
generic term referring to the set of NGN protocol
recommendations produced by ITU-T SG11, without
formal description of the relationship among the NGN
Protocol Set, the NGN Release, and the NGN
Capability Set. However, an overview recommendation
is needed to ensure that the meaning and relationship ofthe NGN Protocol Set with the NGN Capability Set is
clearly understood both inside and outside the ITU.
Such a document would be useful for industry and
would provide a guide to the scope and context of theNGN protocol recommendations.
To define the concept of NGN Protocol Set, this paper
proposes to map NGN Capability Sets to NGN Protocol
Sets simply with a one-to-one correspondence because
the NGN Capability Set 1 was already defined in ITU-T
Rec. Y.2006 and Draft Recommendation of NGN
Capability Set 2 is now available. In this context, NGNProtocol Set 1 includes all protocols for the support of
NGN Capability Set 1, and the scope of NGN Protocol
Set 1 is determined by the scope of NGN Capability Set
1. Similarly, NGN Protocol Set 2 covers all protocols to
support NGN Capability Set 2, and the scope of NGN
Protocol Set 2 is determined by the scope of NGNCapability Set 2. Therefore, ITU-T NGN-Protocol Set 1
includes protocols for the support of NNI and UNI
session control, Resource Control Interfaces, and
Network Attachment Interfaces. NGN Protocol Set 2
will cover all the protocols in NGN Protocol Set 1 and
additionally all other protocols necessary to provideIPTV service.
5. Future Work on NGN Signaling
After successful development of the initial version of
the NGN Protocol Set 1 during the last Study Period
(2005~2008), ITU-T SG11 will continue to develop
NGN protocols during the present Study Period(2009~2012) to consolidate the initial versions on the
basis of feedback from first NGN release
implementations and new requirements. SG11 will
address various additional features and consider
initiating work in the scope of NGN Protocol Set 2.
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The followings are future works to be done for the NGN
protocol development:
Development of the signaling architecture andrequirements to support the NGN Release 2
architecture and IPTV.
Session control requiring further work on SIP-basedprofiles to improve interoperability at UNI and at
NNI, as well as for supporting more simulated
services and even more NGN-native services and
applications. Bearer control for support of IPTV and multicast
data delivery services, for support of more efficient
transfer capabilities such as flow state aware transfercapability.
Resource control for developing additional interfaceprotocols fitting with the RACF enhanced
architecture.
Development of signaling requirements andprotocols to support NGN network attachment, user
identification, number portability, and mobility
procedures to both service and transport stratum.
Development of signaling protocols to supportEmergency Telecommunications Service (ETS),
Telecommunications Disaster Relief (TDR), andearly warning systems as well as NGN testing and
security
Development of test specifications for protocols,
services, and QoS of the NGN to ensure the
compatibilities of equipment, services, and signalingand protocols.
Development of test specifications for Network
aspects of Identification systems including RFID
(NID) and Ubiquitous Sensor Network (USN).
6. Conclusion
In this paper, we introduced overview and functional
architecture of ITU-T NGN, and presented signalingarchitecture and protocols for the ITU-T NGN. In
addition, we discussed the concepts of NGN Release,
NGN Capability Set, and NGN Protocol Set, and listed
future work items for the NGN protocol development.
REFERENCES
[1] ITU-T Recommendation Y.2001 (12/2004), General overview ofNGN.
[2] IETF RFC 3261 (2002), SIP: Session Initiation Protocol.[3] ITU-T Recommendation Y.2012 (09/2006), Functional
requirements and architecture of the NGN release 1.
[4] N. Morita, H. Imanaka, O. Kamatani, T. Oba, and K. Tanida,Overview and Status of NGN Standardization Activities atITU-T, NTT Technical Review, Vol. 5, No. 11, 2007.
[5] N. Morita and H. Imanaka, ITU-T NGN Release 1 Ready,NTT Technical Review, Vol. 6, No. 11, 2008.
[6] ITU-T Recommendation Q.3300 (01/2008), Architectural
framework for the Q.33xx series of Recommendations.[7] ITU-T Recommendation Q.3030 (02/2008), Signalling
architecture for the NGN service control plane.
[8] W3C Recommendation (2007), Simple Object Access ProtocolVersion 1.2.
[9] IETF RFC 2616 (1999), Hypertext Transfer Protocol HTTP/1.1.
[10]IETF RFC 3588 (2003), Diameter Base Protocol.[11]ITU-T Recommendation H.248.1 (09/2005), Gateway Control
Protocol: Version 3.
[12]ITU-T Recommendation Q.700, (03/1993), Introduction toCCITT Signalling System No.7.
[13]ITU-T Recommendation Y.2111 (11/2008), Resource andadmission control functions in Next Generation Networks.
[14]O. Kamatani, K. Kawakami, and S. Yamamoto, Standardization
Activities for Resource and Admission Control Functions in Next
Generation Networks, NTT Technical Review, Vol. 6, No. 12,2008.
[15]ITU-T Recommendation Q.3302.1 (03/2007), Resource controlprotocol No.2 Protocol at the Rp interface between transport
resource control physical entities.[16]IETF RFC 2748 (2000), The COPS (Common Open Policy
Service) Protocol.
[17]IETF RFC 3084 (2001), COPS Usage for Policy Provisioning(COPS-PR).
[18]IETF RFC 3410 (2002), Introduction and ApplicabilityStatements for Internet Standard Management Framework.
[19]ITU-T Recommendation Y.2014 (05/2008), Network attachmentcontrol functions in Next Generation Networks.
[20]IETF RFC 2865 (2000), Remote Authentication Dial In User
Service (RADIUS).[21]ITU-T Recommendation Y.2006 (02/2008), Description of
capability set 1 of NGN release 1.
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